Conventionally, in regard to signal detection methods, signal searching methods, which have an object of detecting areas within a stored signal which is similar to the target signal, are known (for example, refer to “High-speed Signal Searching Method, Apparatus, and Recording Medium Thereof” of Patent Document 1).
However, in the method of this Patent Document 1, since only local pruning (pruning refers to the exclusion of candidates as areas which should be collated without performing collation) was used, in a case where a large stored signal was made the target, there was a shortcoming in that a long time was required for the search.
Furthermore, in regard to other signal detection methods, a signal searching method resulting from global pruning using a L2 distance, which is the Euclidean distance, for measuring the similarity between feature vectors is known (for example, refer to “Signal Detection Method, Signal Detection Apparatus, Recording Medium, and Program” of Patent Document 2).
Here, the L2 distance d2 is normally defined by the formula (1) shown below, and the like. In formula (1), if the feature vectors are represented by X and Y, then X=(x1, . . . , XN), and Y=(y1, . . . , YN).
                                          d            2                    ⁡                      (                          X              ,              Y                        )                          =                                            ∑                              i                =                1                            N                        ⁢                                          (                                                      x                    i                                    -                                      y                    i                                                  )                            2                                                          (        1        )            
However, in the method of this Patent Document 2, because the method of using the L1 distance measure in global pruning was not clear, there was a shortfall in that a search based solely on the L1 distance, which is often highly accurate compared to the L2 distance, could not be performed.
Here, the L1 distance d1 used in the present invention is a distance based on the linear difference between xi and yi in the abovementioned feature vectors, and is defined by the formula (2) below.
                                          d            1                    ⁡                      (                          X              ,              Y                        )                          =                              ∑                          i              =              1                        N                    ⁢                                                                x                i                            -                              y                i                                                                                    (        2        )            
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2000-312343.
[Patent Document 2] Japanese Patent No. 3574075.